A droplet sensor includes an optical cover that forms part of a spheroid, a major axis of the spheroid being a vertical axis, a light emitting/receiving device disposed at a position offset from a first focal point of the spheroid along the major axis, and a reflector disposed in vicinity of a second focal point of the spheroid. The optical cover has an effective detection area between the light emitting/receiving device and the reflector. The effective detection area satisfies a total internal reflection condition at an interface with a gas, and does not satisfy the total internal reflection condition at an interface with a liquid. The reflector reflects, towards a light receiving surface of the light emitting/receiving device, light totally reflected by the effective detection area, or reflects, towards the effective detection area, light directly incident on the reflector from the light emitting/receiving device.

A droplet sensor includes an optical cover having a curved surface that forms a part of a spheroid, a protective film that covers the curved surface of the optical cover, a light source provided at a first focal point of an ellipse facing the curved surface, and a photodetector provided at a second focal point of the ellipse. The refractive index of the protective film is greater than the refractive index of a liquid to be detected. A sensing region is determined by a range of an incident angle at which a light beam emitted from the light source and incident onto the curved surface is totally reflected at the interface between the protective film and a gas, and is not totally reflected at the interface between the protective film and the liquid to be detected.

A device for detecting rain includes a camera and a lighting source for emitting visible light onto a window. The camera and the lighting source are configured and arranged in such a way that the camera can detect a signal of the visible light which the lighting source emits onto the window. The signal which is detected by the camera correlates with visible light of the lighting source, which visible light is reflected or scattered at the inner face of the window or outer face of the window and/or at the raindrop. The visible light passes through a shutter device which causes the light to be blocked or highly attenuated in a predefined direction perpendicular to the illumination direction of structures of the shutter device. In contrast, the light in the direction perpendicular to the predefined direction and to the illumination direction can propagate virtually unimpeded through the shutter device.

A droplet sensor has an optical cover with a curved surface that forms a part of a spheroid, a light source positioned at a first focal point of an ellipse, the first focal point facing the curved surface, and a photodetector positioned at a second focal point of the ellipse. The ellipse has an eccentricity determined such that the curved surface has an effective detection area that satisfies conditions for total internal reflection at an interface with a gas and that does not satisfy the conditions for total internal reflection at an interface with a liquid.

A droplet sensor includes an optical cover having a curved surface that forms a part of a spheroid, a protective film that covers the curved surface of the optical cover, a light source provided at a first focal point of an ellipse facing the curved surface, and a photodetector provided at a second focal point of the ellipse. The refractive index of the protective film is greater than the refractive index of a liquid to be detected. A sensing region is determined by a range of an incident angle at which a light beam emitted from the light source and incident onto the curved surface is totally reflected at the interface between the protective film and a gas, and is not totally reflected at the interface between the protective film and the liquid to be detected.

A droplet sensor has an optical cover with a curved surface that forms a part of a spheroid, a light source positioned at a first focal point of an ellipse, the first focal point facing the curved surface, and a photodetector positioned at a second focal point of the ellipse. The ellipse has an eccentricity determined such that the curved surface has an effective detection area that satisfies conditions for total internal reflection at an interface with a gas and that does not satisfy the conditions for total internal reflection at an interface with a liquid.

A droplet sensor includes an optical cover that forms part of a spheroid, a major axis of the spheroid being a vertical axis, a light emitting/receiving device disposed at a position offset from a first focal point of the spheroid along the major axis, and a reflector disposed in vicinity of a second focal point of the spheroid. The optical cover has an effective detection area between the light emitting/receiving device and the reflector. The effective detection area satisfies a total internal reflection condition at an interface with a gas, and does not satisfy the total internal reflection condition at an interface with a liquid. The reflector reflects, towards a light receiving surface of the light emitting/receiving device, light totally reflected by the effective detection area, or reflects, towards the effective detection area, light directly incident on the reflector from the light emitting/receiving device.

According to various embodiments, there is provided a sensor arrangement including a filter configured to provide an output signal having an output wavelength, the output wavelength having a dependence on a temperature of the filter; a temperature module configured to change the temperature of the filter; a controller circuit configured to control the temperature module for changing the temperature of the filter until the output wavelength increases with decreasing temperature; and a determination circuit configured to determine a dew point of an environment surrounding the sensor arrangement, based on a minimum value of the output wavelength and the dependence.

A device for detecting rain on a pane includes a camera, a lighting source for emitting light and a diffusion element. The light emitted by the lighting source is diffused through and emerges as a light sheet from the diffusion element. The camera, the lighting source and the diffusion element are configured and arranged so that the camera can detect a signal from an image of the light sheet that is emitted by the lighting source, diffused through the diffusion element, impinges on the pane and is reflected or scattered by the pane and/or a raindrop on the pane. The signal detected by the camera is evaluated to detect whether there is rain on the pane.

According to various embodiments, there is provided a sensor arrangement including a filter configured to provide an output signal having an output wavelength, the output wavelength having a dependence on a temperature of the filter; a temperature module configured to change the temperature of the filter; a controller circuit configured to control the temperature module for changing the temperature of the filter until the output wavelength increases with decreasing temperature; and a determination circuit configured to determine a dew point of an environment surrounding the sensor arrangement, based on a minimum value of the output wavelength and the dependence.